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[3.12] gh-127371 Avoid unbounded growth SpooledTempfile.writelines (GH-127372) #130885

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Merged
Yhg1s merged 1 commit into from
Mar 5, 2025
Merged

[3.12] gh-127371 Avoid unbounded growth SpooledTempfile.writelines (GH-127372) #130885

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gh-127371 Avoid unbounded growth SpooledTempfile.writelines (GH-127372) 
(cherry picked from commit cb67b44)

Co-authored-by: Bert Peters <bert@bertptrs.nl>
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@bertptrs @miss-islington
bertptrs authored and miss-islington committed Mar 5, 2025
commit 05290bc29cac48ed1599043d5590ff2349f241e6
12 changes: 8 additions & 4 deletions Lib/tempfile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -848,10 +848,14 @@ def write(self, s):
return rv

def writelines(self, iterable):
file = self._file
rv = file.writelines(iterable)
self._check(file)
return rv
if self._max_size == 0 or self._rolled:
return self._file.writelines(iterable)

it = iter(iterable)
for line in it:
self.write(line)
if self._rolled:
return self._file.writelines(it)

def detach(self):
return self._file.detach()
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28 changes: 28 additions & 0 deletions Lib/test/test_tempfile.py
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Expand Up @@ -1288,6 +1288,34 @@ def test_writelines(self):
buf = f.read()
self.assertEqual(buf, b'xyz')

def test_writelines_rollover(self):
# Verify writelines rolls over before exhausting the iterator
f = self.do_create(max_size=2)

def it():
yield b'xy'
self.assertFalse(f._rolled)
yield b'z'
self.assertTrue(f._rolled)

f.writelines(it())
pos = f.seek(0)
self.assertEqual(pos, 0)
buf = f.read()
self.assertEqual(buf, b'xyz')

def test_writelines_fast_path(self):
f = self.do_create(max_size=2)
f.write(b'abc')
self.assertTrue(f._rolled)

f.writelines([b'd', b'e', b'f'])
pos = f.seek(0)
self.assertEqual(pos, 0)
buf = f.read()
self.assertEqual(buf, b'abcdef')


def test_writelines_sequential(self):
# A SpooledTemporaryFile should hold exactly max_size bytes, and roll
# over afterward
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Security/2024-11-28-20-29-21.gh-issue-127371.PeEhUd.rst
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@@ -0,0 +1,3 @@
Avoid unbounded buffering for :meth:`!tempfile.SpooledTemporaryFile.writelines`.
Previously, disk spillover was only checked after the lines iterator had been
exhausted. This is now done after each line is written.